The present application is based on and claims priority from Japanese Patent Applications 2001-97181, filed Mar. 29, 2001 and 2002-27949, filed Feb. 5, 2002, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a turbine pump that is suitable to a fuel pump to be mounted in a fuel tank of an automotive vehicle.
2. Description of the Related Art
U.S. Pat. No. 5,468,119 or its corresponding publication JP-A-299983 discloses a turbine pump or peripheral pump for a fuel pump to be mounted in an automotive vehicle. The disclosed turbine pump has an outer ring at the circumference of an impeller, which is disposed in chamber walls or a pump casing. The outer ring is disposed outside the spaces (hereinafter referred to the impeller grooves) between blades of the impeller in the radial direction. The outer ring, which is disposed around the impeller grooves, has axial end surfaces flush with the axial end surfaces of the blades. The outside diameter of the impeller is larger than the outside diameter of a pump passage that is formed in the casing and the outer ring is located close to the axial end surface of the pump casing.
In such a turbine pump, the axial distance between the impeller and the casing is arranged to be between several micrometers (xcexcm) and tens of micrometers to prevent high-pressure fuel from leaking from the outlet side of the pump to the inlet side thereof.
While the turbine pump is operating, the impeller moves in the axial direction due to the reaction of the pumping operation. Accordingly, the axial end surface of the outer ring of the impeller contacts the peripheral end surface of the casing.
Because the outer ring is located at the outermost portion of the impeller, the circumferential speed is so high that the outer ring is subject to wear, which lowers pumping capacity and the lifetime thereof.
Therefore, the present invention has been made in view of the above problems.
It is a main object of the invention to provide a reliable turbine pump which prevents the outer ring from wearing.
According to a main feature of the invention, an impeller of a turbine pump has a plurality of blades disposed in the circumferential direction thereof, a plurality of impeller partitions respectively disposed between every two of the blades thereby forming a plurality of impeller grooves at front and rear sides of the partitions and an outer ring disposed at the peripheral edge of the blades. Each impeller groove, each pump passage and the outer ring form a circular space for circulating fuel thereby pressuring and discharging the fuel. The outside diameter of the impeller is smaller than the outside diameter of the pump passages. Therefore, the peripheral portion of the impeller is disposed within the pump passages where the impeller does not contact any surface of the pump passages. It is more preferable that the axial ends of the outer ring are positioned within axial ends of the blades. In addition, the outer ring may have axial ends that are tapered off in the radially inward direction.